Current surgical procedures utilizing catheters are generally extremely disruptive and may cause a great deal of damage to healthy tissue. Quite typically, the desired target area is very small, or relatively small, while the ablation end or edge of the catheter is much larger, causing unneeded damage. In recent years, development of products has been directed with an emphasis on minimizing the traumatic nature of traditional surgical procedures.
Various types of ablation instruments exist in the prior art, including mechanical, electrical, thermal, radio frequency. Conventionally, the various types of ablation instruments have specified uses and/or specialties allowing various methods/procedures to be used with the various types of ablation instruments.
These conventional instruments use catheter-based heat sources for the intended purpose of inducing thrombosis and controlling hemorrhaging within certain body lumens. Detailed examples of local energy delivery devices and related procedures such as those of the types described above are disclosed in the following references: U.S. Pat. No. 4,672,962; U.S. Pat. No. 4,676,258; U.S. Pat. No. 4,790,311; U.S. Pat. No. 4,807,620; U.S. Pat. No. 4,998,933; U.S. Pat. No. 5,035,694; U.S. Pat. No. 5,190,540; U.S. Pat. No. 5,226,430; U.S. Pat. No. 5,292,321; U.S. Pat. No. 5,449,380; U.S. Pat. No. 5,505,730; U.S. Pat. No. 5,558,672; U.S. Pat. No. 5,562,720; U.S. Pat. No. 4,449,528; U.S. Pat. No. 4,522,205; U.S. Pat. No. 4,662,368; U.S. Pat. No. 5,078,736; and U.S. Pat. No. 5,178,618, the contents of which are incorporated by this reference.
Other conventional devices and methods electrically couple fluid to an ablation element during local energy delivery for treatment of abnormal tissues. Some such devices couple the fluid to the ablation element for the primary purpose of controlling the temperature of the element during the energy delivery. Other such devices couple the fluid more directly to the tissue-device interface either as another temperature control mechanism as a carrier or medium for the localized energy delivery. Examples of ablation devices which use fluid to assist in electrically coupling electrodes to tissue are disclosed in the following references: U.S. Pat. No. 5,348,554; U.S. Pat. No. 5,423,811; U.S. Pat. No. 5,505,730; U.S. Pat. No. 5,545,161; U.S. Pat. No. 5,558,672; U.S. Pat. No. 5,569,241; U.S. Pat. No. 5,575,788; U.S. Pat. No. 5,658,278; U.S. Pat. No. 5,688,267; U.S. Pat. No. 5,697,927; U.S. Pat. No. 5,722,403; U.S. Pat. No. 5,769,846; PCT Patent Application Publication No. WO 97/32525; and PCT Patent Application Publication No. WO 98/02201, the contents of which are incorporated by this reference.
Other examples of conventional mechanical devices use a probe as a surgical device in order to allow the physician to directly apply an electrode to tissue. Detailed examples of surgical probes are disclosed in the following references: U.S. Pat. No. 6,023,638; U.S. Pat. No. 4,841,979; U.S. Pat. No. 4,917,096; and U.S. Pat. No. 6,152,920, the contents of which are incorporated by this reference.
While U.S. Pat. No. 5,766,190 discloses a rotating mechanical, or rotational ablation device wherein one or more diamond plated burrs are attached to a driveshaft, which rotates at high speed driven by an advancer/turbine assembly, the contents of which are incorporated by this reference. The driveshaft is provided with a quick connection/disconnection feature allowing for removal of the burr/driveshaft assembly portion of the device from the advancer turbine assembly portion of the device.
As well, other medical devices are known for removing abnormal deposits from corporal channels. For example, U.S. Pat. No. 4,990,134, and U.S. Pat. No. 4,445,509 describe a rotating mechanical system for removing plaque from an artery, the contents of which are incorporated by this reference. U.S. Pat. No. 4,990,134 discloses the use of an ellipsoidal cutting head, or burr, coated with abrasive material such as tiny diamond chips. The cutting head rotates at such a tip velocity that the cutting head generates microscopic particles (on the order of 5 microns or less) and leaves behind a tissue base having a smooth appearance on the surface of the wall of the vessel from which an abnormal deposit has been removed.
Further, U.S. Pat. No. 5,938,670 discloses an ablation device that includes a releasably joinable drive and catheter assemblies, the contents of which are incorporated by this reference. The drive assembly includes a tachometer assembly and a regulator for monitoring and controlling ablating burr speed. Various embodiments disclose an ablating burr that is operatively connected to a catheter tube by drive gears or releasable threads. A radiopaque member is included on the distal end of the catheter tube rendering it visible to an observer.
U.S. Pat. No. 6,527,769 discloses an ablation device assembly which is adapted to form a conduction block along a length of tissue between two predetermined locations along the left atrial wall, the contents of which are incorporated by this reference. The assembly comprises an ablation element on an elongated ablation member that is coupled to each of two delivery members allowing the delivery members to controllably position and secure the ablation element along the length of tissue between the predetermined locations. A linear lesion in the tissue between the predetermined locations is then formed by actuation of the ablation element. Also, the ablation member may slideably engage one or two delivery members such that an adjustable length of the ablation element along the ablation member may be extended externally from the engaged delivery member and along a length of tissue.
Further, surgical procedures also utilize electromagnetic ablation devices.
U.S. Pat. No. 6,958,062 discloses a multiple antenna ablation apparatus including an electromagnetic energy source, a trocar including a distal end, and a hollow lumen extending along a longitudinal axis of the trocar, and a multiple antenna ablation device with three or more antennas, the contents of which are incorporated by this reference. The antennas are initially positioned in the trocar lumen as the trocar is introduced through tissue. At a selected tissue site the antennas are deployable from the trocar lumen in a lateral direction relative to the longitudinal axis. Each of the deployed antennas has an electromagnetic energy delivery surface of sufficient size to, (i) create a volumetric ablation between the deployed antennas, and (ii) the volumetric ablation is achieved without impeding out any of the deployed antennas when 5 to 200 watts of electromagnetic energy is delivered from the electromagnetic energy source to the multiple antenna ablation device. The multiple antenna ablation device is connected to the electromagnetic energy source by a cable.
U.S. Pat. No. 5,785,705 discloses an radio frequency (RF) ablation apparatus that has a delivery catheter with a delivery catheter lumen and a delivery catheter distal end, the contents of which are incorporated by this reference. A first RF electrode is positioned in the delivery catheter lumen. The first RF electrode has a distal end, RF conductive surface, and a lumen. A second RF electrode has a distal end. The second RF electrode is at least partially positioned in the lumen of the first catheter, with its distal end positioned at the exterior of the first RF electrode distal end. An RF power source is coupled to the first and second RF electrodes.
U.S. Pat. No. 5,843,020 discloses an RF ablation device that has a delivery catheter with distal and proximal ends, the contents of which are incorporated by this reference. A handle is attached to the proximal end of the delivery catheter. The delivery catheter has an electrode deployment system whereby the electrode includes a retractable tip section comprising a deployable electrode with portion of one side having a sharp edge.
U.S. Pat. No. 6,508,815 discloses an apparatus and method for use in performing ablation of organs and other tissues includes a radio frequency generator which provides a radio frequency signal to ablation electrodes, the contents of which are incorporated by this reference. The power level of the radio frequency signal is determined based on the subject area of ablation. The radio frequency signal is coupled with the ablation electrodes through a transformation circuit. The transformation circuit includes a high impedance transformation circuit and a low impedance transformation circuit. The high or low impedance transformation circuit is selected based on the impedance of the ablation electrodes in contact with the subject tissue. Measurements of vacuum level, impedance level, resistance level, and time are monitored during an ablation procedure. Values outside of established parameters operate to stop the ablation procedure.
Further descriptions of RF ablation electrode designs conventionally known are disclosed in U.S. Pat. No. 5,209,229; U.S. Pat. No. 5,487,385; and WO 96/10961. the contents of which are incorporated by this reference. Still further, other conventional energy emitting ablation elements are disclosed in U.S. Pat. No. 4,641,649 (microwave ablation); and U.S. Pat. No. 5,156,157 (laser ablation), the contents of which are incorporated by this reference.
Conventional concern in perform surgical procedures includes ensuring that the ablation procedure is complete and not overdone. Complete ablation procedure includes extending ablation through the thickness of the tissue to be ablated before the application of ablation energy is stopped. U.S. Pat. No. 6,648,883 refers to this cut/ablation depth/completion as “transmural” ablation, the contents of which are incorporated by this reference. Conventional methods for detecting transmural ablation include monitoring a desired drop in electrical impedance at the electrode site as disclosed in U.S. Pat. No. 5,562,721, the contents of which are incorporated by this reference. Other indicators are disclosed in U.S. Pat. No. 5,558,671 and U.S. Pat. No. 5,540,684.
A factor in lesion size is tissue temperature. Accordingly, a thermistor or thermal sensor is commonly used to monitor the probe temperature in an effort to monitor the eventual lesion size. RF lesion heat is generated within the tissue; the temperature monitored will be the resultant heating of an electrode or probe by the lesion. A temperature gradient may extend from the lesion to the probe tip, so that the probe tip is slightly cooler than the tissue immediately surrounding it, but substantially hotter than the periphery of the lesion because of the rapid attenuation of heating effect with distance within the lesion.
U.S. Pat. No. 6,648,883 discloses a system and method for creating lesions and assessing their completeness or transmurality by monitoring the impedance of the tissue being ablated, the contents of which are incorporated by this reference. The system monitors for an impedance measurement that is stable at a predetermined level for a certain time, rather than attempting to detect a desired drop or a desired or increased impedance.
In these conventional devices, current spreads out radially from the electrode tip, so that current density is greatest next to the tip, and decreases progressively at distances from it. The frictional heat produced from ionic agitation is proportional to current, i.e., ionic density. Therefore, the heating effect is greatest next to the electrode and decreases further from it.
However, difficulties still exist in surgical or other procedures requiring application of ablation to a target area. In RF lesion ablation, a high frequency alternating current flows from the electrode into the tissue. Tissue heat generated is produced by the flow of current through the electrical resistance offered by the tissue. The greater this resistance, the greater the heat generated.
Accordingly, a need exists for an ablation instrument that can provide greater access and precision to the target area while providing a partial isolation of the target area.